This invention relates generally to automotive vehicle electrical circuits. More specifically, it relates to an electrical circuit that creates daytime running lights by automatically illuminating the vehicle's headlights at reduced intensity when the vehicle is running and the headlight switch is off.
Running lights have been used on automotive vehicles for many years. Running lights on the exterior of the vehicle are connected in circuit with a switch on the interior of the vehicle that is under the control of the vehicle operator. In a truck or highway tractor, these lamps, which are sometimes called clearance, or marker, lamps, are illuminated whenever the operator turns the headlight switch on to illuminate the parking lights and/or the headlights. As such, these clearance, or marker, lamps are actuated to function principally as nighttime running lights because they are illuminated only at times when the parking lights or headlights are turned on. In the past, government regulations have established certain criteria for the operation and performance of such nighttime running lights.
Further extensions of government regulation mandate daytime running light systems on automotive vehicles. In general, these extensions of the regulations require the automatic illumination of daytime running lamps whenever the vehicle is running. Compliance can be accomplished either by placing additional lamps on the vehicle that are devoted exclusively to daytime running or by utilizing presently existing exterior lamps and making appropriate circuit modifications to assure proper daytime illumination intensity. For example, it is contemplated that operation of a vehicle's existing headlights at reduced voltage can provide suitable daytime running illumination intensity.
The incorporation of additional lamps which function exclusively as daytime running lights is probably the simplest to implement from an electrical circuit standpoint. However, other considerations make this approach undesirable, especially for vehicles which have already been designed. First, new lamps must be fabricated and mounted at suitable locations on the existing vehicle. This will undoubtedly require extensive design and re-tooling services. The additional lamps are also a significant added cost. Therefore, the utilization of a vehicle's existing lamps, such as the headlights, is preferable for incorporating the daytime running light feature.
Unfortunately, this more desirable approach tends to complicate the electrical circuitry that is used. This is because the integration of the daytime running light function must not interfere with other functions that are to be performed by the particular lamps chosen to perform daylight running. Thus, operation of the headlights at reduced illumination intensity to provide daytime running lights must not otherwise interfere with the ability of the headlights to be turned on at full intensity by the headlight switch, nor interfere with the high beam/low beam operation of the headlamps.
While the extended government regulations are addressed to newly manufactured vehicles, the possibility of retrofitting vehicles already in service is a consideration in the implementation of a daytime running light circuit. A circuit that can be compactly packaged and conveniently installed in existing vehicles is a desirable attribute.
Certain published regulations concerning daytime running lights are generally stated as requiring daytime running lights to be automatically turned on whenever the vehicle is running and the headlight switch is off. However, no specific means are given for how these two conditions, i.e. vehicle running and headlight switch off, are to be sensed, nor how the desired running light function is to be performed in consequence of these two conditions.
The present invention relates to a daytime running light circuit that is especially well suited for integration with existing exterior illumination systems of an automotive vehicle, and specifically in the disclosed embodiment, integration with the existing headlight circuit of the vehicle. Accordingly, the invention is readily compatible both as original equipment in new vehicles and for retrofit of many vehicles already in service. Moreover, the circuit of the present invention can be fabricated with a comparatively small number of conventional individual circuit devices. These devices can be conveniently packaged for expeditious installation in both new and older vehicles. The invention possesses novel and unique features which individually and collectively contribute to its attributes.
The circuit of the invention contemplates a unique means for sensing running of the vehicle. Contemporary automotive electrical systems comprise alternators, driven by the engine, that produce the electrical power for the electrical systems. The alternator output is operatively coupled by means of a regulator with the vehicle battery, or batteries, to maintain proper charge. A typical automotive alternator has a further terminal that is commonly referred to as the "R" terminal, and it is this "R" terminal that is used in the present inventIon to provide an indication that the vehicle is running.
When the alternator is being driven, a certain voltage is present at the "R" terminal. For a twelve-volt alternator, the "R" terminal output is six volts. But this voltage is present at the "R" terminal only after the engine has been started and is running. In other words, during the engine start cycle, no voltage is present at the "R" terminal, and it is only after the engine is running on its own and driving the alternator that voltage appears at the "R" terminal. The present invention advantageously utilizes this "R" terminal voltage as an indicator of vehicle running.
However, the fact that the engine is running is not necessarily conclusive that the vehicle is in motion. For example, the vehicle may be parked with the engine running, and in such a case, it may be deemed unnecessary to operate the daytime running lights. Accordingly, extended regulations have recognized that the daytime running lights need not necessarily come on until the vehicle transmission is placed in gear and/or an associated parking brake is released.
The circuit of the present invention utilizes the voltage at the alternator "R" terminal as an indication of running of the vehicle, and depending upon whether it is desired to illuminate the headlights while the engine is running and the vehicle parked, provision may be made for also interlocking the daytime running light circuit with associated transmission and/or parking brake switch(es).
The disclosed embodiment of the invention comprises essentially two relays, a switch, and a resistor for integration with the existing headlight circuit of the vehicle. Use of such a comparatively few number of components helps to keep down the cost of incorporating the daytime running light feature. The particular manner in which the circuit is organized and arranged with the existing headlight filaments serves to reduce the filament voltage to an appropriate level for meeting daytime illumination intensity requirements without the wastefulness that would be associated with use of additional voltage-reducing resistors or incorporation of a chopper circuit.